A gear pump is a particular type of pump in which a pair of rotating gears move hydraulic fluid. More specifically, the gears have meshing teeth that convey a flow of hydraulic fluid into and through the pump along flow paths extending circumferentially around the gears.
The hydraulic fluid is drawn into the gear pump through a suction hole. When the gears rotate, the gear teeth cause flow rate fluctuations as they move into and out of meshing engagement between the gears. The flow rate fluctuations propagate outward from the suction hole. Corresponding fluctuations in the hydraulic fluid pressure can cause noise. Such noise can be especially undesirable when the gear pump is used in a hydraulic power steering system for a vehicle.